1. Field of the Invention
The present invention relates generally to delta-sigma modulators/converters, and more specifically, to power consumption control in a delta-sigma modulator.
2. Background of the Invention
Delta-sigma modulators are in widespread use in analog-to-digital converters (ADCs) and digital-to-analog converters (DACs), in which they provide very linear behavior and simple implementation due to the reduced number of bits used in the analog signal comparison. Delta-sigma modulators can be implemented with a high level of control of the frequency distribution of “quantization noise”, which is the difference between the ideal output value of the modulator as determined by the input signal and the actual output of the modulator provided by a quantizer. The relative simplicity of the architecture and the ability to finely control the quantization noise makes delta-sigma converter implementations very desirable.
Power consumption in delta-sigma designs is usually dominated by the current requirements of the amplifier in the first integrator stage of the modulator loop filter. The feedback correction signal provided at the input of the first integrator stage contains large magnitude high frequency components. The analog input signal may also contain such high frequency components. The change in the integrator output over a sampling interval is proportionate to the difference between the input signal and feedback correction/noise-shaping signal for that interval. Therefore, the output current capability of the first amplifier must be sufficient to handle the rate of charging of the integrator capacitor for any possible slope (for continuous-time integrators) or step (for discrete-time integrators). Since the changes at subsequent stages of the integrator are dependent on already-integrated versions of the quantizer output, the changes at those integrators are typically smaller. Consequently, the first integrator stage amplifier is typically dominant in the modulator power requirement.
It is generally desirable to lower circuit power requirements, in particular in battery-operated equipment, but in general for reduced heat generation and power supply requirements.
Therefore, it would be desirable to provide a delta-sigma modulator having reduced power requirements.